Various proposals have been made as to diagnostic systems and diagnostic devices. For instance, Japanese translation Publication of PCT International application No. 2003-507088 (Patent Document 1) proposes an evaluation method in cancer diagnosis, in which an tissue to be measured is irradiated with a laser beam from a light source, Raman-scattered light is separated from Rayleigh scattered light by spectrum separation, and a substantial difference between intensity of Raman-scattered light from a biological tissue that may be a malignant tumor and intensity of Raman-scattered light from a neighboring normal biological tissue is evaluated as presence or risk of illness. In addition, JP-A-2002-5835 (Patent Document 2) proposes a method of discernment between a normal tissue and a cancer tissue using Raman spectrum, in which pulse-like near infrared light having a wavelength of 1064 nm from a Nd:YAG laser light source 10 is used as excitation light for irradiating a specimen, and Raman-scattered light split by a spectrometer and detected by a photodetector 31 is counted by a coincidence counting circuit, based on an excitation light detection signal from a photo diode 16 for detecting the excitation light, in synchronization with the excitation light, and hence intensity of background light in the Raman spectrum is reduced.